The present invention concerns radio frequency (RF) filters and pertains particularly to mounting film bulk acoustic resonator filters in microwave packages using flip chip bonding technology.
For applications such as cellular phones, it is desirable to reduce the size of components. Particularly, it is desirable to integrate RF duplexers and filters as part of a radio-on-a-chip with a manufacturable technology.
Bulk acoustic resonators have been used to implement filters. One advantage of using acoustic resonators is that the speed of sound is approximately three or four orders of magnitude smaller than the speed of light, making the wavelengths, and thus the dimensions of a device, small compared with conventional (L-C) tank circuits.
Film bulk acoustic resonator filter die are placed within hermetically sealed packages. In the prior art, wire bonds are used to attach a die to leads of a package.
Flip-chip bonding has been used for making connections between a semiconductor chip and a package. In flip-chip bonding, wire bonds are not run between the chip and the package. Instead, bead-like projections are electrodeposited as terminals around one face of the chip. The face of the chip is then registered with the package terminals and bonded to them.
In accordance with the preferred embodiment of the present invention, a device includes a die that contains a filter circuit. The filter is implemented using film bulk acoustic resonators. A package contains the die. The package includes a base portion. Signal paths are incorporated in the base portion. Solder joints attach the die to the base portion. The solder joints electrically connect pads on the die to the signal paths in the base portion. The solder joints do not include, and are used instead of, wire bonds.
In one preferred embodiment, the package is made of ceramic material and is hermetically sealed. Alternatively, the package may be made of other materials.
Use of the present invention facilitates moving a ground plane closer to the die, thereby reducing mutual inductance. Use of the present invention also results in a large reduction of parasitic inductance due to long bond wires.